| Message ID | 1410257037-20030-1-git-send-email-daniel.thompson@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Dan, After Greg's comment, Am ok with the patch and sorry for the noise. Good that you removed the barier() too. You can have my Ack. --srini On Tue, Sep 9, 2014 at 11:03 AM, Daniel Thompson <daniel.thompson@linaro.org > wrote: > The architectures supported by this driver, arm and sh, have expensive > implementations of writel(), reliant on spin locks and explicit L2 cache > management. These architectures provide a cheaper writel_relaxed() which > is much better suited to peripherals that do not perform DMA. The > situation with readl()/readl_relaxed()is similar although less acute. > > This driver does not use DMA and will be more power efficient and more > robust (due to absence of spin locks during console I/O) if it uses the > relaxed variants. > > The driver supports COMPILE_TEST and therefore falls back to writel() > when writel_relaxed() does not exist. > > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> > Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.com> > Cc: Maxime Coquelin <maxime.coquelin@st.com> > Cc: Patrice Chotard <patrice.chotard@st.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Jiri Slaby <jslaby@suse.cz> > Cc: kernel@stlinux.com > Cc: linux-serial@vger.kernel.org > --- > > Notes: > Changes since v1: > > * Added fallback to writel() to permit COMPILE_TESTing (review > of Greg Kroah-Hartmam). > > drivers/tty/serial/st-asc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c > index 8b2d735..a3fc167 100644 > --- a/drivers/tty/serial/st-asc.c > +++ b/drivers/tty/serial/st-asc.c > @@ -151,12 +151,16 @@ static inline struct asc_port *to_asc_port(struct > uart_port *port) > > static inline u32 asc_in(struct uart_port *port, u32 offset) > { > - return readl(port->membase + offset); > + return readl_relaxed(port->membase + offset); > } > > static inline void asc_out(struct uart_port *port, u32 offset, u32 value) > { > +#ifdef writel_relaxed > + writel_relaxed(value, port->membase + offset); > +#else > writel(value, port->membase + offset); > +#endif > } > > /* > -- > 1.9.3 > >
On 09/09/14 12:08, Srinivas Kandagatla wrote: > Hi Dan, > > After Greg's comment, Am ok with the patch and sorry for the noise. > Good that you removed the barier() too. Yes. I got interested in Greg's question about which architectures don't have readl_relaxed() and, in the process, discovered I was wrong about that being needed anyway. > You can have my Ack. > > --srini > > On Tue, Sep 9, 2014 at 11:03 AM, Daniel Thompson > <daniel.thompson@linaro.org <mailto:daniel.thompson@linaro.org>> wrote: > > The architectures supported by this driver, arm and sh, have expensive > implementations of writel(), reliant on spin locks and explicit L2 cache > management. These architectures provide a cheaper writel_relaxed() which > is much better suited to peripherals that do not perform DMA. The > situation with readl()/readl_relaxed()is similar although less acute. > > This driver does not use DMA and will be more power efficient and more > robust (due to absence of spin locks during console I/O) if it uses the > relaxed variants. > > The driver supports COMPILE_TEST and therefore falls back to writel() > when writel_relaxed() does not exist. > > Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org > <mailto:daniel.thompson@linaro.org>> > Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.com > <mailto:srinivas.kandagatla@gmail.com>> > Cc: Maxime Coquelin <maxime.coquelin@st.com > <mailto:maxime.coquelin@st.com>> > Cc: Patrice Chotard <patrice.chotard@st.com > <mailto:patrice.chotard@st.com>> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org > <mailto:gregkh@linuxfoundation.org>> > Cc: Jiri Slaby <jslaby@suse.cz <mailto:jslaby@suse.cz>> > Cc: kernel@stlinux.com <mailto:kernel@stlinux.com> > Cc: linux-serial@vger.kernel.org <mailto:linux-serial@vger.kernel.org> > --- > > Notes: > Changes since v1: > > * Added fallback to writel() to permit COMPILE_TESTing (review > of Greg Kroah-Hartmam). > > drivers/tty/serial/st-asc.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c > index 8b2d735..a3fc167 100644 > --- a/drivers/tty/serial/st-asc.c > +++ b/drivers/tty/serial/st-asc.c > @@ -151,12 +151,16 @@ static inline struct asc_port > *to_asc_port(struct uart_port *port) > > static inline u32 asc_in(struct uart_port *port, u32 offset) > { > - return readl(port->membase + offset); > + return readl_relaxed(port->membase + offset); > } > > static inline void asc_out(struct uart_port *port, u32 offset, u32 > value) > { > +#ifdef writel_relaxed > + writel_relaxed(value, port->membase + offset); > +#else > writel(value, port->membase + offset); > +#endif > } > > /* > -- > 1.9.3 > >
diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c index 8b2d735..a3fc167 100644 --- a/drivers/tty/serial/st-asc.c +++ b/drivers/tty/serial/st-asc.c @@ -151,12 +151,16 @@ static inline struct asc_port *to_asc_port(struct uart_port *port) static inline u32 asc_in(struct uart_port *port, u32 offset) { - return readl(port->membase + offset); + return readl_relaxed(port->membase + offset); } static inline void asc_out(struct uart_port *port, u32 offset, u32 value) { +#ifdef writel_relaxed + writel_relaxed(value, port->membase + offset); +#else writel(value, port->membase + offset); +#endif } /*
The architectures supported by this driver, arm and sh, have expensive implementations of writel(), reliant on spin locks and explicit L2 cache management. These architectures provide a cheaper writel_relaxed() which is much better suited to peripherals that do not perform DMA. The situation with readl()/readl_relaxed()is similar although less acute. This driver does not use DMA and will be more power efficient and more robust (due to absence of spin locks during console I/O) if it uses the relaxed variants. The driver supports COMPILE_TEST and therefore falls back to writel() when writel_relaxed() does not exist. Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org> Cc: Srinivas Kandagatla <srinivas.kandagatla@gmail.com> Cc: Maxime Coquelin <maxime.coquelin@st.com> Cc: Patrice Chotard <patrice.chotard@st.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: kernel@stlinux.com Cc: linux-serial@vger.kernel.org --- Notes: Changes since v1: * Added fallback to writel() to permit COMPILE_TESTing (review of Greg Kroah-Hartmam). drivers/tty/serial/st-asc.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) -- 1.9.3